2025-05-04 19:24:03 +02:00
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use std::sync::Mutex;
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2025-05-04 01:04:46 +02:00
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use crate::body::Body;
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2025-05-04 19:24:03 +02:00
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use rayon::prelude::*;
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2025-05-04 01:04:46 +02:00
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const G: f64 = 6.67430e-11;
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pub struct Simulator {
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pub bodies: Vec<Body>,
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pub time: f64,
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pub timestep: f64,
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}
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pub fn distance_squared(a: [f64; 2], b: [f64; 2]) -> f64 {
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let dx = a[0] - b[0];
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let dy = a[1] - b[1];
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dx * dx + dy * dy
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}
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impl Simulator {
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pub fn new(timestep: f64) -> Self {
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Self {
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bodies: Vec::new(),
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time: 0.0,
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timestep,
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}
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}
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pub fn add_body(&mut self, body: Body) {
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self.bodies.push(body);
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}
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pub fn step(&mut self) {
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let dt = self.timestep;
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2025-05-04 19:24:03 +02:00
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let n = self.bodies.len();
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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#[derive(Clone)]
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struct State {
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position: [f64; 2],
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velocity: [f64; 2],
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}
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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let original_states: Vec<State> = self
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.bodies
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.iter()
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.map(|b| State {
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position: b.position,
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velocity: b.velocity,
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})
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.collect();
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let masses: Vec<f64> = self.bodies.iter().map(|b| b.mass).collect();
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fn compute_accelerations(states: &[State], masses: &[f64]) -> Vec<[f64; 2]> {
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let n = states.len();
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let accels = (0..n).map(|_| Mutex::new([0.0, 0.0])).collect::<Vec<_>>();
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(0..n).into_par_iter().for_each(|i| {
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for j in (i + 1)..n {
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let dx = states[j].position[0] - states[i].position[0];
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let dy = states[j].position[1] - states[i].position[1];
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let dist_sq = dx * dx + dy * dy;
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let dist = dist_sq.sqrt();
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if dist < 1e-3 {
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continue;
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}
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let force = G * masses[i] * masses[j] / dist_sq;
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let ax = force * dx / dist;
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let ay = force * dy / dist;
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{
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let mut a_i_lock = accels[i].lock().unwrap();
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a_i_lock[0] += ax / masses[i];
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a_i_lock[1] += ay / masses[i];
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}
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{
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let mut a_j_lock = accels[j].lock().unwrap();
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a_j_lock[0] -= ax / masses[j];
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a_j_lock[1] -= ay / masses[j];
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}
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2025-05-04 01:04:46 +02:00
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}
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});
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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accels
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.into_iter()
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.map(|mutex| mutex.into_inner().unwrap())
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.collect()
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}
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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// RK4 Stufen
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let k1_pos = original_states.iter().map(|s| s.velocity).collect::<Vec<_>>();
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let k1_vel = compute_accelerations(&original_states, &masses);
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let mut temp_states = original_states
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.iter()
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.enumerate()
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.map(|(i, s)| State {
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position: [
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s.position[0] + k1_pos[i][0] * dt / 2.0,
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s.position[1] + k1_pos[i][1] * dt / 2.0,
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],
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velocity: [
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s.velocity[0] + k1_vel[i][0] * dt / 2.0,
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s.velocity[1] + k1_vel[i][1] * dt / 2.0,
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],
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})
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.collect::<Vec<_>>();
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let k2_pos = temp_states.iter().map(|s| s.velocity).collect::<Vec<_>>();
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let k2_vel = compute_accelerations(&temp_states, &masses);
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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for i in 0..n {
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temp_states[i].position[0] = original_states[i].position[0] + k2_pos[i][0] * dt / 2.0;
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temp_states[i].position[1] = original_states[i].position[1] + k2_pos[i][1] * dt / 2.0;
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temp_states[i].velocity[0] = original_states[i].velocity[0] + k2_vel[i][0] * dt / 2.0;
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temp_states[i].velocity[1] = original_states[i].velocity[1] + k2_vel[i][1] * dt / 2.0;
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}
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2025-05-04 19:24:03 +02:00
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let k3_pos = temp_states.iter().map(|s| s.velocity).collect::<Vec<_>>();
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let k3_vel = compute_accelerations(&temp_states, &masses);
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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for i in 0..n {
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temp_states[i].position[0] = original_states[i].position[0] + k3_pos[i][0] * dt;
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temp_states[i].position[1] = original_states[i].position[1] + k3_pos[i][1] * dt;
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temp_states[i].velocity[0] = original_states[i].velocity[0] + k3_vel[i][0] * dt;
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temp_states[i].velocity[1] = original_states[i].velocity[1] + k3_vel[i][1] * dt;
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}
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2025-05-04 19:24:03 +02:00
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let k4_pos = temp_states.iter().map(|s| s.velocity).collect::<Vec<_>>();
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let k4_vel = compute_accelerations(&temp_states, &masses);
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// Finale Updates
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for i in 0..n {
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let body = &mut self.bodies[i];
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let old_position = body.position;
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body.position[0] += (dt / 6.0)
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* (k1_pos[i][0] + 2.0 * k2_pos[i][0] + 2.0 * k3_pos[i][0] + k4_pos[i][0]);
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body.position[1] += (dt / 6.0)
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* (k1_pos[i][1] + 2.0 * k2_pos[i][1] + 2.0 * k3_pos[i][1] + k4_pos[i][1]);
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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body.velocity[0] += (dt / 6.0)
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* (k1_vel[i][0] + 2.0 * k2_vel[i][0] + 2.0 * k3_vel[i][0] + k4_vel[i][0]);
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body.velocity[1] += (dt / 6.0)
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* (k1_vel[i][1] + 2.0 * k2_vel[i][1] + 2.0 * k3_vel[i][1] + k4_vel[i][1]);
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2025-05-04 01:04:46 +02:00
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2025-05-04 19:24:03 +02:00
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// Bewegung loggen
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let dx = body.position[0] - old_position[0];
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let dy = body.position[1] - old_position[1];
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let movement = (dx * dx + dy * dy).sqrt();
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if i == 1 {
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println!("Earth moved {:.6} meters", movement);
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}
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2025-05-04 01:04:46 +02:00
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}
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self.time += dt;
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}
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}
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